The present invention relates to a method of making an improved grip for golf clubs and other devices employing handles that are subject to shock when such devices are impacted, as for example, golf clubs, tennis ball racquets, racquetball racquets, baseball bats, and hammers.
There have previously been developed resilient grips which successfully reduce shock to the muscle and arm joints of the users of golf clubs, tennis racquets, racquet ball racquets, baseball bats and other impact imparting devices. See, for example, U.S. Pat. No. 5,797,813 granted to applicant Aug. 25, 1998. Such earlier grips utilize a polyurethane layer bonded to a felt layer to define a strip which is spirally wrapped around the handle of a golf club, racquet or the like to conform to the external configuration of such handle, or in the case of a golf club, a resilient underlisting sleeve which is slipped onto the handle of a golf club.
In such grips the polyurethane material provides tackiness to resist slippage by a wet or sweaty hand, while both the polyurethane as well as the felt contribute to the overall cushioning effect of the grip. The felt material additionally serves as a substrate for the manufacture of the polyurethane layer when a xe2x80x98wet coagulationxe2x80x99 method is employed, wherein the polyurethane is applied directly to the felt as the felt is drawn through the various manufacturing stages in a continuous process. Coagulation of the polyurethane takes place after its deposition on the felt which causes it to become intimately joined with the felt fibers. Such coagulation also forms closed pores in the polyurethane layer which assists in providing a cushioning effect of the grip.
While prior art polyurethane/felt grips have been developed that provide the desired shock absorption properties, the felt material is prone to absorbing water. Accordingly, the grip will tend to absorb the perspiration from the user""s hand and may become saturated during play thereby causing slippage of the golf club or tennis racquet in the user""s hands. The same problem occurs under wet conditions such as when playing golf in the rain. In an effort to address this problem, the present invention proposes the use of EVA (ethylene-vinyl acetate copolymer) as a substitute for the felt substrate. The use of EVA as a substitute for felt can also reduce the weight of a grip up to one-half the weight of a conventional polyurethane/felt grip. Such reduction of grip weight will reduce the total weight of a golf club, as well as provide an increase in the swing weight of the club. With previously used polyurethane/EVA grips the polyurethane layer of such grip is made by a xe2x80x98dry coagulationxe2x80x99 method wherein the thickness of the polyurethane layer that can be produced is severely limited. The conventional dry coagulation method requires the polyurethane to first be applied to a paper strip on which it is allowed to air dry to become coagulated, Upon coagulation, the paper is stripped from the polyurethane and a layer of EVA material and an adhesive is applied directly to the coagulated polyurethane. Such method limits the thickness of the polyurethane to a thickness of about 0.10 mm and therefore limits the size of any pores which may be formed in the coagulated polyurethane and hence the amount of shock absorption provided by a grip made by such method. By contrast, a polyurethane/felt grip utilizing a xe2x80x9cwet coagulation method,xe2x80x9d such as described in my aforementioned U.S. Pat. No. 5,797,813, can provide a polyurethane layer having a thickness of up to 1.5 mm, and with such polyurethane layer being formed with closed pores that extend through a substantial portion of the polyurethane layer. These pores make it possible for the grip to readily absorb the shock created when a golf ball is struck by a golf club.
A method of making a polyurethane/EVA grip is therefore needed that is capable of producing a tacky grip having a greater degree of cushioning or shock absorption than is available from currently available polyurethane/EVA grips made by dry coagulation methods, and with such grip having the light-weight and water excluding characteristics of a grip utilizing EVA. Additionally, a method of manufacture is needed for economically making such improved grip.
The present invention is directed to a method for making polyurethane/EVA grips wherein the polyurethane layer of such grip can have a thickness of up to 1.5 mm, whereby pores can be formed in the polyurethane layer when such layer is coagulated so as to provide a polyurethane/EVA grip having the shock absorbing characteristics of a polyurethane/felt grip. Additionally, such method permits the precise ratio of the thicknesses of the polyurethane and EVA layers to be determined for a particular grip application in terms of the tackiness and shock cushioning characteristics of the grip material.
More particularly, a preferred method of the present invention provides for the use of a nylon cloth for the temporary support of polyurethane during a wet coagulation of the polyurethane, the raw polyurethane material being applied to the nylon cloth in a continuous fashion through the various steps of such method. After coagulation of the polyurethane is complete, the coagulated polyurethane is separated from the nylon cloth and joined with an EVA substrate by an adhesive layer, again in a continuous manner. It has been found that the use of a nylon cloth and the wet coagulation of the polyurethane allows a significantly thicker layer of polyurethane to be formed than is possible with dry coagulation of the polyurethane. The polyurethane layer can be made as tacky and supple as desired to provide an appropriate amount of tackiness for the grip, while the polyurethane and EVA combination can provide the desired amount of shock cushioning. Moreover, the use of an EVA substrate provides a grip which will not absorb water.
The features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment which, taken in conjunction with the accompanying drawings, which illustrate by way of example the principles of the invention.